By Ted R. Hunt, Chief Trial Attorney, Jackson County Prosecutor’s Office, Kansas City, Missouri
dvances in DNA technology over the last decade require police departments to take a new approach to how potentially critical evidence at a crime scene is located and identified. Cellular DNA, or “touch DNA,” as it is commonly referred to, is now routinely collected by many police agencies during the course of their investigations. Touch DNA consists of skin cells shed by a suspect during the commission of a crime on surfaces that were touched. It is now possible for investigators or scientists to collect cellular material at a crime scene and identify a suspect through subsequent DNA analysis.
The critical question, however, is how can evidence that is invisible to the naked eye be located and collected before the scene is released and the evidence is forever lost? The answer to that question is based on understanding the basic components of physical evidence; asking victims, witnesses, and suspects the right questions during an investigation; and sharing that information with crime scene investigators before the evidence is lost, diminished, or destroyed.
What Makes Something Physical Evidence?
Physical evidence is composed of three separate elements: (1) its contextual characteristics and circumstantial significance at a crime scene; (2) what those in a position to know—witness(es), victim(s), or suspect(s)—say (or do not say) about it; and (3) the forensic testing results, conclusions, and weight (quantitative or qualitative) that can be attributed to a match or association.
These three elements correlate with the work performed by three types of investigative assets employed by most departments to identify, collect, and analyze such evidence—crime scene investigators (CSIs), detectives, and forensic scientists.
Challenges to Identifying Relevant Touch DNA Evidence
There are a number of challenges inherent in the identification, designation, and collection of touch DNA evidence. One challenge relates to the division of labor assigned to investigative assets within most police agencies (CSIs, detectives, DNA analysts). Although these assets may work on the same investigation, they may not be aware of information possessed by the other assets involved, leading to gaps in understanding. A second and related problem occurs when time-sensitive and location-specific information is not immediately shared among those investigative assets. A third challenge relates to the nature of touch DNA evidence itself—which cannot be observed by the naked eye and for which no preliminary test exists to determine its presence.
A brief analysis of how the traditional investigative process works (and does not work well at times) highlights some of the difficulties encountered with the identification, designation, and collection of touch DNA evidence.
|Left: Using a swab to collect trace amounts of cellular material, or touch DNA, from the handle of a knife. Middle: Swabbing a doorknob for cellular material. Right: The collection device is packaged in a paper envelope to avoid degrading or destroying the cellular material.|
Crime Scene Investigators
Crime scene investigators typically respond to scenes for the purpose of documenting and collecting evidence. Unlike case detectives, their contact and interaction with victims, witnesses, and suspects is often very limited or non-existent. Any preprocessing information about the scene or its contents typically comes second-hand. In addition, CSIs working a scene may have little opportunity to provide detectives—who are concurrently interviewing victims, witnesses, and suspects—with information about the scene and its contents. Thus items with unclear significance— those that outwardly do not appear to be “out of place” or related to the crime—may go uncollected by crime scene investigators who have no information to the contrary.
In reality, a select number of those items may have critical significance to the case. However, that information may be known only to detectives and may not become known to crime scene investigators (if at all) until after the scene is released and the relevant items are lost, compromised, or destroyed. As a result, CSIs often make important decisions regarding probative evidence based on logical inferences and observation rather than case-specific information. Accordingly, due to this lack of information regarding circumstantial significance, crime scene investigators will typically (and understandably) over-collect items of potential evidence.
In fact, much of what crime scene investigators routinely collect is not actually “evidence” in the true sense of the word. Rather, these items are recovered in the event that new information may establish relevance. In the absence of time-sensitive and location-specific information from investigative interviews, CSIs are largely confined to an informational vacuum when assessing the value of items or surfaces that may contain probative cellular material.
As a result of this communication deficit, touch DNA samples with no connection to the crime may be collected. Their subsequent analysis may result in false investigative leads or worse—reasonable doubt at trial. Equally troubling is the fact that a touch DNA sample that might have associated the true perpetrator with the crime may never be identified, located, or collected.
Detectives are normally responsible for acquiring information from persons’ of interest; those who were in a position to provide information about the events that occurred during a crime. Typically, however, these individuals are quickly removed from the crime scene and taken to a separate location, such as a hospital or police headquarters to be treated or interviewed.
In an effort to quickly develop a lead and make an arrest in unknown suspect cases, the focus of investigative questioning is likely to center on “whodunnit” rather than “howdunnit.” Although these questions are certainly a critical and necessary part of an investigation, they are not, standing alone, sufficient to effectively solve crimes in this post-DNA era.
Another difficulty brought about by investigative division of labor is that, in many cases, the detective(s) who interviewed the victim, witnesses, and/or the suspect may have never set foot inside the crime scene. As a result, those officials may be completely unaware of the existence or significance of the physical items or surfaces discovered. Therefore, critical questions about items of potential interest at the scene—known at that time only to crime scene investigators—may go unasked and unanswered.
Laboratory analysts typically receive physical items submitted by the case detective who may request testing of one or more (and possibly dozens) of submitted items. However, in cases involving complex forensic scenes, the detective may have little, if any, information about why certain objects, items, or substances were collected or processed by CSIs in the first place, or how they relate to the crime under investigation.
This information, which provides contextual relevance to the submitted items, will likely not be known to the DNA analyst. Analysts typically do not respond to the scene, read the investigative reports, or interview the witnesses. Thus, DNA analysts may be asked to perform DNA testing on swabs recovered from items or surfaces about which they have little, if any, specific information. The net effect is that the investigative value of information derived from unfocused analysis of numerous touch samples may be at best unclear and at worst misleading.
Police agencies can take a number of actions to improve their chances of identifying and collecting relevant touch DNA evidence before it is lost or destroyed. First, they should develop an intra-agency protocol that sets forth written guidelines to be followed by each investigative asset—crime scene investigators, detectives, and lab analysts—when attempting to identify, designate, and collect potential touch DNA evidence.
Second, in addition to questioning aimed at describing the suspect, detectives must also routinely ask victims, witnesses, and suspects questions that focus on what particular items, objects, or surfaces may have been touched or handled by the suspect during the commission of the crime.
Third, information derived by detectives from investigative interviews should be immediately relayed—in real time—to crime scene investigators before the scene is released to the owner or the public. This will allow items or surfaces that may otherwise appear insignificant to be collected and processed. In this way, crime scene investigators will have the opportunity to collect and process all items that have been transformed into evidence based on information that lends context. Expedited use of this information will facilitate intelligence-based crime scene processing that will enhance the identification, collection, and preservation of probative touch DNA samples.
Fourth, crime scene investigators must communicate with detectives and share information about the presence of items and surfaces that appear to possess either obvious or ambiguous significance. This may generate further investigative questioning that may, in turn, lead to the identification, collection, and processing of additional probative crime scene samples.
Fifth, crime scenes should not be released until detectives have fully advised crime scene investigators of relevant scene-specific information derived from witness interviews.
Sixth, detectives, crime scene investigators, and laboratory analysts should routinely meet during and/or immediately at the conclusion of an investigation. The purpose of this meeting is to collectively make informed, targeted DNA testing decisions based on
- the investigative question in need of an answer;
- the relevance of available samples;
- intelligence gathered by detectives—which may enhance, diminish, or negate the relevance of those samples; and
- an assessment of both the capabilities and the limitations of available DNA technologies.
In conclusion, better coordination and real-time communication among key investigative assets are essential to maximizing opportunities for the identification, designation, and collection of relevant touch DNA evidence at crime scenes. Coordination and communication are best facilitated by departmental procedures that promote the targeted acquisition and immediate sharing of time-sensitive and location-specific information among investigative partners. This information must be shared before a crime scene is released and potential evidence is compromised, lost, or destroyed. Follow-up meetings between detectives, CSIs, and lab analysts should provide a forum for making informed testing decisions. These decisions should focus on identifying the most probative and scientifically promising samples available—in light of existing forensic technologies and capabilities—with an eye toward answering the critical investigative questions. ♦
Please cite as:
Ted R. Hunt, "Communication, Context, and Crime Scenes: Enhancing Opportunities to Identify and Collect Touch DNA Evidence," The Police Chief 80 (September 2013): 42–43.